I just installed a decent used pair of Progressive 430s obtained from a member here. They're 11.5" - and it made a considerable difference in the ride quality over the tired OEM Showa units. Very happy with the road feel and more solid behavior. Didn't realize how soft the OEMs had gotten.
I've lowered lots of bikes and only one needed to go back up a bit (a VMax). But, on the Valkyrie, my initial ride did not reveal any negatives. Much improved - and definitely lower. I had thought about slipping the fork tubes half an inch or so, but I don't think it's needed. I am not normally a peg scraper, so I don't think that'll be a problem.
Has anyone experienced any true negatives at 11.5" on a Tourer?
